The 25-year-old midfielder Brazilian is wanted at Arsenal, who want to sign him on loan for the rest of the campaign.
The Gunners have an agreement in place with the player and have reportedly offered to pay his full wages during his loan stint at the Emirates.
Arsenal are waiting for Juventus to agree to loan him out but it seems Allegri is not in favour of letting the midfielder go in the ongoing transfer window.
The Juventus coach stressed the importance of keeping the current squad together for the rest of the season if they are to achieve their goals this year.
“I have already said this”, Allegri said in a press conference when asked about Arthur’s future.
“This is the Juventus squad and these are the players we must have until the end of the season for the best possible result.
“And the best possible result is reaching the top four of Serie A and progress in the Champions League, and on Tuesday there is the Italian cup.”
Juventus are believed to be wanting to sign a replacement first before agreeing to loan out Arthur.
They are interested in Chelsea’s Ruben Loftus-Cheek but Thomas Tuchel has ruled out loaning him out this month.